1. Field of the Invention
The present invention relates to the manufacture of filters for cigarettes and more particularly to the making of grooves in cigarette filters.
2. Description of the Prior Art
Cigarettes are often provided with filter devices at one end to remove materials from the smoke stream coming from the tobacco column during smoking. These filters, which are attached to the tobacco column, come in many different sizes, shapes and forms. Some filters which are presently on the market include grooves. In some filter constructions, the grooves facilitate the by-passing of smoke around the filter. In other filter constructions, the grooves provide a channel for mixing ventilating air and by-passed smoke. In stilll other constructions, the grooves provide a path for only ventilating air to pass therealong without mixing with smoke.
In the manufacture of grooved cigarette filters, many suggestions have been made for making the grooves in the filter rod. U.S. Pat. No. 3,804,695 shows the use of a pair of parallel rollers in pressure engagement defining a nip therebetween wherein one of the rollers is provided with a circumferential or a helical grooved surface so that, as a filter rod passes therethrough, permanent depressions are made along the longitudinal dimensions of the filter rod. U.S. Pat. No. 4,075,936 shows a die having cam manipulated radially reciprocating pins that periodically move into and out of the longitudinal path of a filter rod as the filter rod tow moves past. When the pins extend into the path of the tow they impress grooves in the filter rod. U.S. Pat. No. 4,149,546 shows an apparatus for making grooves in a cigarette filter wherein a filter rod is moved in an arcuate path transverse to a heated forming means, the filter rod being supported and conveyed for relative movement at the periphery of a drum-shaped inner rotor and the forming means compresses a heated arcuate outer strator element or elements projecting inwardly toward the rotor. U.S. Pat. No. 4,324,540 teaches an apparatus for making grooves in filters which comprises a plurality of fixed position groove forming blades and a filter plug conveying device located next to the groove forming blades. Cigarette filters to be grooved are moved along the path between the conveyor device and blades, rolling past the blades whereupon grooves are formed in the filters by the blades.